The present invention relates to a trigger valve apparatus preferably employed in a pneumatic tool, such as a nailar or a similar pneumatic tool.
FIG. 17 shows a conventional pneumatic fastener. FIG. 18 shows a trigger valve apparatus employed in the pneumatic fastener shown in FIG. 17.
A trigger valve 106 comprises a plunger 107 shiftable in an axial direction in response to a movement of a trigger 139, and a valve piston 109 shiftable in an opposed direction in response to the shift movement of the plunger 107. The valve piston 109 directly controls compressed air supplied to or discharged from a sleeve valve chamber 108. The trigger valve 106 further comprises valve bushes 110 and 111 supporting the plunger 107 and the valve piston 109 so as to be slidable in the axial direction thereof. A spring 112 is interposed between the plunger 107 and the valve piston 109.
An air passage 116 connects a valve piston chamber 113 and the atmosphere. An O-ring 125, provided at a lower portion of the plunger 107, selectively opens or closes the air passage 116 in accordance with a shift movement of the plunger 107. An air passage 114 connects an accumulator chamber 102 to the valve piston chamber 113. An O-ring 115, provided on a cylindrical surface of an axial bore of the valve piston 109, selectively opens or closes the air passage 114 in response to a shift movement of the plunger 107. An air passage 120 connects the accumulator chamber 102 to the sleeve valve chamber 108 located below a sleeve valve 119. An O-ring 121 selectively opens or closes the air passage 120 in accordance with a shift movement of the valve piston 109. An air passage 147 connects the air passage 120 to the atmosphere. An O-ring 123 selectively opens or closes the air passage 147 in accordance with a shift movement of the valve piston 109. An O-ring 124, coupled around the valve piston 109, seals a clearance between the valve piston 109 and the bush 110. Thus, the valve piston chamber 113 is always isolated from the air passage 147 by the O-ring 124.
When the valve piston 109 is positioned at its top dead center, the accumulator chamber 102 communicates with the sleeve valve chamber 108 while the sleeve valve chamber 108 is isolated from the atmosphere because the air passage 147 is closed by the O-ring 123 as shown in FIG. 19. When the valve piston 109 is positioned at its bottom dead center, the sleeve valve chamber 108 communicates with the atmosphere via the air passage 147 while the sleeve valve chamber 108 is isolated from the accumulator chamber 102 by the O-ring 121 as shown in FIG. 20.
A sleeve valve portion 126, serving as a main valve, comprises a sleeve valve 119, a sleeve valve rubber 127, a sleeve valve spring 128, an exhaust rubber 130, and O-rings 131 and 132. The sleeve valve rubber 127 is coupled around an upper end portion of the sleeve valve 119 so as to selectively connect or disconnect the cylinder 103 to or from the accumulator chamber 102. The sleeve valve spring 128 resiliently urges the sleeve valve 119 toward its top dead center. An air passage 129 is provided for exhausting compressed air from an upper space of the piston 104a of the cylinder 103. The exhaust rubber 130 is coupled with the upper portion of the cylinder 103 and selectively brought into contact with the sleeve valve 119 to open or close the air passage 129. The O-rings 131 and 132 are provided to always isolate the sleeve valve chamber 108 from the air passage 129.
When the sleeve valve 119 is lowered, the sleeve valve 119 is brought into contact with the exhaust rubber 130 to close the air passage 129 while the accumulator chamber 102 communicates with the upper space of the piston 104a in the cylinder 103. When the sleeve valve 119 is raised, the upper end of the cylinder 103 is closed and the sleeve valve 119 separates from the exhaust rubber 130 to open the air passage 129. The air passage 129 communicates with the atmosphere via an air passage (not shown).
A return air chamber 133, provided around a lower portion of the cylinder 103, stores compressed air to return the driver blade 104b to its top dead center. An air passage 135, having a check valve 134, is provided near an axial center of the cylinder 103. An air passage 136 is provided at the lower portion of the cylinder 103. A piston bumper 137 is located near the lower end of the cylinder 103. The piston bumper 137 absorbs excessive energy of the driver blade 104b after the driver blade 104b has struck the nail 105.
An operating portion 138 comprises a trigger 139 operated by a user, an arm plate 140 positioned between the trigger 139 and the plunger 107, and a push lever 142 extending from the lower end of a nose 141 to the vicinity of the arm plate 140. The push lever 142 is resiliently urged toward the nose 141 and slidable along the nose 141. The plunger 107 is raised upward only when the trigger 139 is pulled by the user and the push lever 142 is shifted against the resilient force with the tip of the push lever 142 being pressed to a member into which the nail 105 is struck.
Hereinafter, an operation of the above-described pneumatic fastener 101 will be explained with reference to FIGS. 17 through 21.
FIGS. 17 and 18 show the pneumatic fastener 101 and the trigger valve 106 in a condition where the accumulator chamber 102 is filled with compressed air. Part of the compressed air stored in the accumulator chamber 102 flows into the valve piston chamber 113 via the air passage 114. The plunger 107 is positioned at its bottom dead center as it receives a differential force caused by a diameter difference between the O-ring 115 and the O-ring 125 as well as a resilient force of the spring 112. Furthermore, part of the compressed air stored in the accumulator chamber 102 flows into the sleeve valve chamber 108 via the air passage 120. The sleeve valve 119 is positioned at its top dead center as it receives a differential force caused by a diameter difference between the sleeve valve rubber 127 and an O-ring 146 as well as another differential force caused by a diameter difference between the O-ring 131 and the O-ring 132 in addition to a resilient force of the sleeve valve spring 128.
FIG. 19 shows a condition of the trigger valve 106 at a moment where the plunger 107 is positioned at its top dead center. The O-ring 115 closes the air passage 114. The valve piston chamber 113 communicates with the atmosphere via the air passage 116. So, the compressed air can go out of the valve piston chamber 113.
FIG. 20 shows a condition of the trigger valve 106 at a moment where the valve piston 109 has moved at its bottom dead center in response to the shift movement of the plunger 107 to its top dead center.
When the pressure in valve piston chamber 113 is substantially equalized with the atmospheric pressure, the valve piston 109 receives a differential force caused by a diameter difference between the O-ring 121 and the O-ring 124 and therefore shifts to its bottom dead center against the resilient force of the spring 112. The O-ring 121 closes the air passage 120. The sleeve valve chamber 108 communicates with the atmosphere via the air passages 120 and 147. The compressed air is exhausted from the sleeve valve chamber 108.
When the pressure in the sleeve valve chamber 108 is substantially equalized with the atmospheric pressure, the sleeve valve 119 receives a differential force caused by a diameter difference between the sleeve valve rubber 127 and the O-ring 146 and therefore starts shifting toward its bottom dead center against the resilient force of the sleeve valve spring 128. When the accumulator chamber 102 communicates with the cylinder 103, the sleeve valve 119 receives a differential force caused by a diameter difference between the O-ring 146 and the exhaust rubber 130. Therefore, the sleeve valve 119 rapidly moves to its bottom dead center.
The exhaust rubber 130 closes the air passage 129. The accumulator 102 communicates with the cylinder 103. The compression air rushes into the upper space of the piston 104a in the cylinder 103 from the accumulator chamber 102. The piston 104a rapidly shifts downward to its bottom dead center. The driver blade 104b integrated with the piston 104a strikes the nail 105 into a wood or similar member. The air residing under the piston 104a in the cylinder 103 flows into the return air chamber 133 via the air passage 136. After the piston 104a has passed the air passage 135, part of the compressed air residing above the piston 104a flows into the return air chamber 133 via the air passage 135.
FIG. 21 shows a condition the trigger valve 106 at a moment where the plunger 107 has returned to its bottom dead center. The plunger 107 shifts to its bottom dead center in response to a pressing force of the compressed air in the accumulator chamber 102 as well as the resilient force of the spring 112. The O-ring 125 closes the air passage 116. The compressed air rushes into the valve piston chamber 113 from the accumulator chamber 102 via the air passage 114.
When the compressed air flows into the valve piston chamber 113, the valve piston 109 receives an upward force F1 proportional to a diameter difference (b−a) between the O-ring 124 (diameter=b) and the O-ring 115 (diameter=a) as well as a downward force F2 (<F1) proportional to a diameter difference (b−c) between the O-ring 124 (diameter=b) and the O-ring 123 (diameter=c) in addition to an upward force given by the spring 112.
Therefore, the valve piston 109 shifts to its top dead center. The O-ring 123 disconnects the air passage 120 from the air passage 147. The accumulator chamber 102 communicates with the sleeve valve chamber 108 via the air passage 120. Thus, the compressed air flows into the sleeve valve chamber 108.
When the compressed air flows into the sleeve valve chamber 108, the sleeve valve 119 receives a differential force caused by a diameter difference between the O-ring 131 and the O-ring 146 as well as the resilient force of the sleeve valve spring 128. Therefore, the sleeve valve 119 shifts to its top dead center. When the sleeve valve 119 has reached its top dead center, the sleeve valve rubber 127 isolates the cylinder 103 from the accumulator chamber 102. The exhaust rubber 130 opens the air passage 129. So, the cylinder 103 communicates with the atmosphere. The compressed air stored in the return air chamber 133 pushes the piston 104a upward. The piston 104a rapidly moves toward its top dead center. The air residing in the upper space of the piston 104a is exhausted to the outside (i.e., the atmosphere) via the air passage 129.
According to the arrangement of the above-described conventional pneumatic fastener, the compressed air in the valve piston chamber 113 exits to the outside (i.e., the atmosphere) via the air passage 116. The compressed air in the sleeve valve chamber 108 exits to the outside (i.e., the atmosphere) via the air passage 147. In other words, the exhaust passages for the compressed air are provided near the trigger 139. This in not desirable in that the exhaust air blows fingers of the user.
U.S. Pat. No. 3,808,620 discloses a remote valve arrangement for a pneumatic tool according to which compressed air actuating a trigger valve is exhausted toward a trigger. Thus, user's fingers are subjected to the exhaust air.